An initial pilot project was performed which determined the applicability of fluorescently labelling a partially purified von Willebrand factor preparation for the use in binding studies with platelets using flow cytometry. Although binding of the labeled material was demonstrated, the subsequent inhibition studies showed sensitivity too low for usefulness in experiments on plasma levels of von Willebrand factor. U973 cells have also been investigated by flow cytometry to investigate two different aspects of cell surface antigen expression. In the first set of experiments, regulation and expression of CD4 antigen was compared to 4B4 and 2H4 antigens after treatment in culture with the phorbol ester, PMA. 2H4 is not expressed. Although CD4 is down-regulated after PMA treatment is constant or increased. These characteristics were also studied in a series of U937 subclones. In the second set of experiments, the binding of urokinase and tissue plasminogen activator were measured using fluorescent antibody techniques. This involved not only U937 c ells but HUVEC endothelial, cells as well. Major emphasis has been to establish a primary research effort to investigate the lipo-protein-associated coagulation inhibitor (LACI). After development of a factor Xa-inhibition based chromogenic assay for LACI, purification of LAI, using published techniques was initiated. This required the growth and harvest of liter quantities of hepatoma cell line (HEPG2) conditioned serum-free medium as the source of human LACI. The purification used CdC1 precipitation, affinity chromatography on Sepharose-bound factor Xa, and gel filtration. This purification yielded microgram amounts of LACI and established parameters for future scaled-up processing.